From February 7th, a number of Ubisoft games will become completely unplayable while the company transitions between data servers. The server switch will affect customers because of a particularly aggressive digital rights management (DRM) system found in the publisher's older titles. The system, called uPlay, connects to a server each time a game is loaded to ensure the software is genuine, and as the servers will be down, affected games won't play. Assassin's Creed and Splinter Cell: Conviction for Mac and Tom Clancy's HAWX 2 for Windows PCs are the standout games on the list of unplayables this week. DRM found in more recent titles only requires a one-time activation on first launch, so as long as your title has been verified before the 7th, you'll be able to play as normal, albeit without online play.
Also down will be all of Ubisoft's websites, barring its customer support pages and forums, which the company had the foresight to transition before the upcoming downtime. A press release from the publisher apologizes, but makes no mention of how long the transition will take, instead recommending customers follow the official Ubisoft Twitter account. Ubisoft will keep online play going for a select few games, but that will come as no consolation to the users that have paid for a game that they won't be able to play, online or offline, for an unknown length of time.
You can find a complete list of affected (and unaffected) titles in the source link below.